Method and apparatus for automatic multi-run welding

ABSTRACT

This invention relates to a method and apparatus for automatic multi-run welding of a joint such as a square butt joint, a V-type joint, or a U-type joint, etc. This invention incorporates a sensor which moves along the joint and which scans a number of points along portions of the joint. The points scanned are used to calculate the cross-sectional area of the portions of the joint and the cross-sectional areas are then used to determine welding parameters, such as weld speed and weld rod feed, for welding which is to be done in each of the joint portions. Thus, the joint is filled with weld material uniformly along its length despite deviations which may be inherent in the edges of the materials which are being welded.

This is a divisional application of Ser. No. 07/580,378, filed on Sep.10, 1990 now U.S. Pat. No. 5,107,093.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method and the apparatus for automaticmulti-run welding of a joint formed by two joint surfaces, in whichmethod the contour of the joint is scanned by a sensor which emitssignals corresponding to the shape of the joint, which signals, afterevaluation, control the deposition of the weld beads by means of acontinuously fed electrode which is movable in at least threedirections, is directed towards a welding point in the joint by means ofan arc weld head and is moved relatively along the joint.

In welding, account must be taken of the variations in thecross-sectional area of the weld joint along the joint. Thecross-sectional area is determined, on the one hand, by the contour ofthe joint and, on the other hand, by a line which connects the two jointedges. The cross-section of the joint often differs from the idealshape, for example a V-shape, U-shape etc. In the case of long joints,the width of the joint usually varies, and the joint edges are oftenoffset relative to each other. The cross-sectional area along the jointtherefore alters continuously on account of the geometric imperfectionsof the joint, which are essentially caused by production-engineering inthe joint preparation. In automatic welding in particular, it must bepossible for these variations in the joint cross-section along the jointto be recorded, so that the beads can be deposited with a chosen amountof welding material per unit of length, which finally results in a jointwhich is even and filed to the same level. In manual or semi-automaticwelding, the welder can vary the welding parameters, for example thewelding speed, in order to compensate for irregularities in the weldjoint. In the case of automatic welding, such adaption of the welding tothese variations must be effected entirely automatically.

2. Description of the Prior Art

EP-B-12,962 describes a procedure of the type mentioned in theintroduction. On the basis of the actual joint width scanned by asensor, the number of weld beads to be deposited alongside each other isselected automatically, and the transition from one bead to the next iscarried out in accordance with a specific procedure. However, during thewelding, no account is taken of the variations in the cross-section ofthe joint, which cross-section is affected not only by the joint width,but also to a significant extent by the joint offset.

In another proposal, U.S. Pat. No. 4,608,481, the joint is filled bymeans of an oscillating movement of an electrode, and the shape of thejoint is scanned at the same time by means of, for example, measuringthe arc voltage during the oscillating movement at certain relativepositions of the welding burner in relation to the workpiece. Thisprocedure requires additional arrangements for the oscillating movementand separate control equipment for the movement.

OBJECT OF THE INVENTION

The aim of the present invention is to provide a multi-run weldingmethod in which the actual joint cross-section at different portions ofthe joint is taken as the basis for the determination of the weldingparameter or parameters affecting the amount of welding material to bedeposited per unit of length.

SUMMARY OF THE INVENTION

The invention is characterized in that the sensor is oscillated in frontof the weld head at the different portions of the joint and is made tomeasure coordinates, in two directions, of points on the contour of thejoint in question, which points essentially define the cross-section ofthe joint. The two directions chosen are preferably the verticaldirection and the lateral direction of the joint. The area of thepolygon defined by the coordinates of these points measured during thesame oscillating movement is calculated, and welding parameters aredetermined for the joint portions as a function of the correspondingpolygon area. These welding parameters control the amount of weldingmaterial per unit of length to be deposited in a bead in the joint.

For practical reasons, the contour of the joint is scanned in apoint-wise manner. The position of the points is defined by coordinates,preferably in the vertical and lateral directions of the joint. Thepoints become corner points in a polygon, whose area can be easilycalculated. In the case of simple joint shapes with pane joint surfaces,in general, only the coordinates of a small number of points are neededfor calculating the polygon area corresponding to the jointcross-section. It is conceivable to measure these coordinates during ahalf oscillating movement of the sensor, for example by moving thesensor from one joint edge to the other, so that the sensor can scan thecontour of the joint between the joint edges.

The sensor is advantageously moved in synchrony with the weld head, thatis to say with the welding speed. During the oscillating movement of thesensor, the sensor is also moved along the joint, and the oscillatingmovement and the measurement proceed within a specific portion of thejoint. On account of this movement, the various points on the jointcontour measured in the same operation belong to differentcross-sections of the joint. The surface of the calculated polygontherefore becomes a type of mean value for the varying cross-sectionalarea within the joint portion.

The length of the scanned joint portion is a function of the ratiobetween the speed of the oscillating movement and the welding speed. Thegreater the oscillating speed and the lower the welding speed, thesmaller the length is of the scanned joint portion. The shorter thescanned joint portion is, the smaller the variations in thecross-sectional area are within the joint portion.

The measurement method described above for determining a cross-sectionalarea which is a mean value for a specific joint portion has been foundto be completely sufficient for a satisfactory welding result inautomatic multi-run welding.

Within the scope of this invention, it is also conceivable to have thesensor scan a cross-sectional area without the sensor being moved insynchrony with the weld head. This provides a correct value for thecross-sectional area at a specific point in the joint. However, the nextmeasurement can only be carried out a distance further on in the joint,since account must be taken of the continuous movement of the weld head.The individual measurements of the joint cross-section must in this casebe taken as a basis for a mean calculation of the cross-sectional areabetween the different measurement times, and the result is very similarto the result obtained with a sensor moved in synchrony with the weldhead.

Calculation of the polygon area corresponding to the cross-sectionalarea also requires the coordinates of a point on each joint edge. Sincea direct scanning of the position of the joint edges is difficult tocarry out with the sensor, in a preferred embodiment of the inventionthe sensor is made to measure a coordinate in the vertical direction ofa respective point on each topside of the joint. A line is thencalculated between two points on each joint side and the point ofintersection of the line with the plane defined by the topside of thejoint is a point of the joint edge of the corresponding joint side.

According to a preferred embodiment of the invention, the sensor isoscillated during on-going deposition of a weld bead, in which respectat least the first bead is deposited with a certain amount of weldingmaterial per unit of length, which amount is preferably identical alongthe whole joint. It has been found to be advantageous to scan the wholejoint before the welding parameters for the next bead are determined.However, the welding and scanning of the joint should take pacesimultaneously in order to minimize the overall time for the weldingwork. In this regard, the sensor is arranged in front of the weld headand scans the contour of the joint while the first bead is beingdeposited. Therefore, no measurement values are obtained for determiningthe welding parameters for the first bead and the first bead isdeposited with a predetermined amount of welding material per unit oflength, which amount is preferably identical along the whole joint. Itmay be advantageous for practical reasons to initially deposit severalbeads with a certain predetermined amount of welding material.

According to the invention, it is also advantageous for the weldingparameters for each joint portion to be a function of the residual areacalculated for the joint portion, this residual area being thedifference between the calculated polygon area and the correspondingcross-sectional area of the bead being deposited. Thus, when the weldingparameters are determined, the area of the bead which is deposited bythe weld head is calculated from the polygon area scanned by the sensor.In this case it is advantageous for only one welding parameter to bedetermined for each joint portion as a function of the polygon area,namely either the welding speed or the feed speed of the electrode,preferably the welding speed.

According to the invention, it is also advantageous for a welding speedfor deposition of a certain amount of welding material to be determinedcorresponding to the mean value of the polygon areas of the jointportions. It is also advantageous for the welding speed for the variousjoint portions to be calculated as a function of the ratio between thepolygon areas of the joint portion and the mean of the polygon areas. Avalue giving optimum or close to the optimum welding quality is selectedas the mean value. The welding speed in the various joint portions iscalculated with regard to the deviation of the joint portion from themean value. In cases where there are considerable variations in thecontour of the joint, these deviations are also quite considerable. Itis therefore advantageous, according to the invention, for a warningsignal to be triggered when the welding parameter for any joint portionhas a value lying outside a predetermined value range. This value rangeshould include a maximum and minimum value and also the mean value forthe welding parameter. The warning signal informs the operator that, onaccount of the shape of the joint, the welding parameter at one or morejoint portions has a value which indicates that the welding result canno longer be regarded as acceptable. The operator can intervene in theon-going welding work and correct this error in a number of conventionalways which are not covered here.

According to a further embodiment of the invention, the welding speed isa function of the residua area calculated for the joint portion and afunction of the welding speeds which have been calculated for the twoadjoining joint portions. Since only one polygon area is calculated foreach joint portion, there is only a discrete sequence of values ofcalculated welding speeds. For the best weld, the transition betweenthese welding speeds must be effected continuously. For the requiredchange in speed, a suitable acceleration or deceleration is selected, inwhich respect account must be taken of the mass of the material whosespeed is to be changed.

In automatic multi-run welding, the number of beads must be determinedfor each layer. According to one embodiment of the invention, a secondbead is deposited in the joint alongside the first bead in order to forman intermediate layer. This intermediate layer is deposited when themean of values corresponding to the width of the joint, in the variousjoint portions at the level of this intermediate layer, is greater thana predetermined value. Intermediate layer here refers to all weld layersin the joint with the exception of the root layer and the top layer.

it is also advantageous for the value corresponding to the width of thejoint to be equal to a product k.b₁, in which k is a factor between 0.5and 1.0, and b₁ is the joint width at the actual joint base. It is alsoadvantageous that the given width value be a certain distance in thelateral direction of the joint between the electrode tip and the jointsurface. The joint width is determined by the sensor at each jointportion by means of the measured coordinates. As has been describedabove, the measurement method employed provides a certain mean value ofthe width dimension for each joint portion; the width dimension beingthe joint width at the actual joint base. The introduction of only thismean value of the joint width within each joint portion does not inpractice affect the desired result of obtaining an indication of whentwo beads need to be deposited in the joint. The factor k is dependenton the shape of the joint and on the welding parameters, and isdetermined by testing. The distance between the electrode tip and thejoint surface is chosen with regard to the desired penetration zone inthe base material.

The filling of the joint should also be uniform in the case of an edgeoffset. At the joint side with the higher joint edge, a greater amountof welding material must be deposited than at the other joint side.According to the invention, it is advantageous for the polygon definedby the coordinates of the measurement points to be divided by a centerline through the joint into a first and a second subpolygon, whichinclude the measurement points on each respective joint side and jointedge. It is also advantageous for the welding parameters for the weldbead, which is to be deposited against the respective joint side, to bedetermined for the joint portions as a function of the correspondingsubpolygon area. The amount of welding material per unit of length forthe two beads is thus adapted to the actual cross-sectional area of ajoint with varying edge offset.

As has been described above, the deposition of two beads per layer isdetermined only as a function of the width of the joint at the level ofthe layer. In contrast, the deposition of three or more beads per layeris determined as a function of the cross-section of the layer.

According to the invention, it is advantageous for at least three beadsto be deposited in an intermediate layer, when the mean of a value,determined for each joint portion, of the cross-sectional area of thesaid intermediate layer is greater than a predetermined value. It isalso advantageous for the number of beads in the intermediate layer tobe a function of the mean value, and for the cross-sectional area of thethird bead, and where appropriate further beads, in this layer to be afunction of the cross-sectional area of the first two beads in thislayer which are deposited against the joint sides. The calculated valueof the cross-sectional area of the intermediate layer in each jointportion is calculated as a function of the width of the intermediatelayer and the mean value of a measured height h₁ of the bead depositedfirst in this intermediate layer against one of the joint sides at acertain distance from the joint side, and of a calculated height h₂ ofthe bead deposited immediately thereafter against the other joint side,where h₂ =(h₁.a₂)/a₁ and a₁ and a₂ are the cross-sectional areas of thetwo deposited beads.

For determining the number of beads, it is advantageous to start from acalculated value of the area of the intermediate layer. When al thebeads have finally been deposited in this intermediate layer, its actualcross-sectional area generally differs somewhat from the calculatedtheoretical value.

For calculating the theoretical value, the height h₁ is determined bymeans of the sensor, whereas the height h₂ is calculated, since thesensor is not capable of measuring the height of the second bead beforedepositing the third bead, as is explained hereinafter. When calculatingthe cross-sectional area of the intermediate layer, the width dimensionchosen is advantageously a dimension which represents a mean value ofthe joint width at this layer.

For practical reasons, the value of the area of the intermediate layeris also calculated before deposition of the 4th, 5th etc. bead in theintermediate layer in the same way as has been described above with acalculated value of h₂, despite the fact that the actual heightdimension h₂ can be determined before the deposition of these beads.

In the case of an edge offset, in order to achieve an even distributionof the amount of welding material per unit of length in the three ormore beads in the layer, the polygon defined by the coordinates of themeasurement points is divided by a center line through the joint into afirst and a second subpolygon, which include the measurement points ofeach respective joint side and joint edge. The welding parameter for theweld bead which is to be deposited against the one joint side or otherjoint side, respectively, is determined for each joint portion as afunction of the corresponding subpolygon area, and of thecross-sectional area of the last-deposited bead in the underlying layer.The cross-sectional areas for the further beads in the same intermediatelayer are obtained by interpolation with respect to the two beadsalready deposited against the joint sides, and the corresponding weldingspeeds are inversely proportional to the cross-sectional areas. In thecase of an edge offset, the amount of welding material per unit oflength in a joint portion is different in the two outermost beadsdeposited against the joint side. Therefore, in the intermediate beads,an amount of welding material will be deposited which is obtained byinterpolation of the two amounts of welding material which have beendeposited against the joint sides. The corresponding welding speed isinversely proportional to the value of the cross-sectional areacorresponding to the amount of welding material. In this way, thedistribution of the deposited welding material is uniform in the wholelayer.

Before a subsequent layer is deposited, a check is always made toascertain whether this subsequent layer will be a top layer with whichthe welding is finished. According to the invention it is thereforeadvantageous, after deposition of an intermediate layer in the joint andbefore deposition of the next layer, to calculate the quotient from themean value of the polygon areas of the joint portions of the remainingjoint cross-section and the mean value of the cross-sectional areas ofthe last-deposited intermediate layer in all joint portions. It is alsoadvantageous for the beads for a top layer to be deposited in the jointon this intermediate layer when the quotient is less than apredetermined value, preferably less than 0.7, in which respect thenumber of beads in the top layer is preferably increased by one,compared to the number in the last-deposited intermediate layer. Thus,after finishing each layer, a comparison of the value of theabove-mentioned quotient with a predetermined value is carried out todetermine whether the next layer will be a top layer.

The invention will now be described in greater detail with reference tothe attached drawings which shows an exemplary embodiment. Furtheradvantages of the invention will emerge from this description.

One feature of the invention resides broadly in a method for automaticmulti-run welding of a joint formed between at east two adjacent piecesto be welded by a weld head to form a weld, each of the at least twoadjacent pieces comprising a joint surface, each joint surface beingdisposed for being welded to at least one adjacent joint surface, themethod comprising the steps of: scanning at east one joint surface ofthe joint with sensor means, directly measuring by the scanning aplurality of actual points on the at least one joint surface, generatingdata corresponding to coordinates of the plurality of points,calculating with the data to obtain values to determine at east a partof a cross-section of at least a portion of the joint, and alsocalculating at least a part of a cross-sectional area of at least a partof the cross-section, and adjusting at east one of; a speed of feed of asolid welding material being fed into the weld, and a relative speed ofmovement between the weld head and the at east two adjacent pieces, byusing the obtained values to control the amount of solid weldingmaterial deposited along the joint.

Another feature of the invention resides broadly in an apparatus forautomatic multi-run welding of a joint formed between at least twoadjacent pieces to be welded by a weld head to form a weld, each of theat least two adjacent pieces comprising a joint surface, each jointsurface being disposed for being welded to at east one adjacent jointsurface, the apparatus comprising: a welding housing, a weld headdisposed on the welding housing, the weld head comprising a device forreceiving a solid welding medium and a device for feeding the solidwelding medium to the weld, a welding power supply for providing currentfor the weld head, a device for providing relative movement between theweld head and the at least two adjacent pieces, sensor for scanning atleast a portion of the joint, the sensor being for directly measuring aplurality of actual points on at least one joint surface to generatedata corresponding to coordinates of the points, processing device forreceiving the data corresponding to coordinates of the points, forcalculating the cross-sectional area of the joint from the datacorresponding to coordinates of the points, for calculating at east oneof; a speed of feed of the solid welding medium into the weld, and arelative speed of movement between the weld head and the at east twoadjacent pieces, and for producing signals for control of the welding,at least one of; a device for controlling the device for feeding thesolid welding material to control the amount of solid welding materialbeing fed into the weld, and the device for controlling the device forproviding relative movement between the weld head and the at east twopieces to control the amount of solid welding material being depositedalong the joint, and a control device for receiving the signals forcontrol of the welding, and for controlling at least one of the devicefor controlling the device for feeding the solid welding material tocontrol the amount of solid welding material being fed into the weld,and the device for controlling the device for providing relativemovement between the weld head and the at least two pieces to controlthe amount of solid welding material being deposited along the joint.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a, 1b and 1c show a section through a slightly deformed V-typejoint at different times during welding.

FIGS. 2a, 2b and 2c show the edge offset in a butt joint in cylindricalworkpieces.

FIGS. 3a and 3b show two types of square butt joints.

FIG. 4 shows, somewhat diagrammatically, a sensor for scanning a jointcontour, FIG. 4 is a section along IV--IV in FIG. 5.

FIG. 5 shows an overhead view of the same sensor as shown in FIG. 4.

FIG. 6 is a perspective view of a U-type joint.

FIG. 6a shows cross-sectional view of the joint of FIG. 6.

FIG. 7a shows a section through a V-type joint.

FIG. 7b shows the V-type joint of FIG. 7a with the first bead of a weld.

FIG. 8 shows a V-type joint for clarification of certain terms used inthe description.

FIG. 9 shows a diagram of calculated welding speeds in different jointportions.

FIG. 10 shows a correct V-type joint in the case of deposition of alayer with two beads.

FIG. 11 shows a V-type joint with an edge offset, in the case ofdeposition of a layer with two beads.

FIG. 12 shows a diagram of calculated welding speeds for two beads whichare to be deposited in the same layer of a V-type joint with an edgeoffset.

FIG. 13 shows a correct V-type joint in the case of deposition of alayer with three beads.

FIG. 14 shows a V-type joint with an edge offset, in the case ofdeposition of a layer with three beads.

FIG. 15 shows a V-type joint before deposition of a top layer.

FIG. 16 shows diagrammatically an arrangement for automatic multi-runwelding.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1a shows a section through a V-type joint between two workpieces1a, 1b with a gap, 2, joint sides 3a, 3b, joint edges 4a, 4b, root sides5a, 5b and topsides 6a, 6b. The workpieces 1a and 1b are shown slightlyoffset in the vertical direction with respect to the joint edges 4a, 4b.The cross-sectional area A_(o) of the joint is delimited by the jointsides 3a, 3b, the gap 2 and an imaginary line 7 between the two jointedges 4a, 4b.

FIG. 1b shows the same joint with a root bead 8. The cross-sectionalarea of the joint is now smaller and is designated by A₁. In some cases,the penetration of the bead into the base material on the root side ofthe joint is not satisfactory, and an additional root bead must bedeposited. This additional root bead is usually deposited on theunderside of the joint after the complete welding of the rest of thejoint. In this respect, is usual to turn the workpieces over in order tofacilitate the welding work. The question regarding the need for anadditional root bead is not discussed here and does not constitute partof the invention. The root bead 8 is deposited along the whole jointwith fixed welding parameters.

it should be noted that the cross-section of the joint varies along thejoint on account of manufacturing tolerances, especially as regards thejoint width, the edge offset and changes in shape during welding. Whenthe first bead is deposited at a constant welding speed v_(s) and aconstant feed speed v_(e) of the welding electrode, the cross-sectiona_(sn) of the deposited bead is identical along the whole joint, namelya_(sn) =(a_(e).v_(e))v_(s), in which a_(e) is the cross-sectional areaof the welding electrode. After the first bead is deposited, thecross-sectional area A_(o) of the joint at the position examineddecreases to A₁ =A_(o) -a_(s1) or, in general terms, the cross- sectionat a position n of the joint becomes A_(1n) =A_(on) -a_(s1n). As hasalready been stated, A_(1n) varies along the whole joint. FIG. 1c showsthe same joint after deposition of a further three beads 9, 10, 11. Theremaining cross-sectional area becomes A₄ =A_(o) -(a_(s1) +a_(s2)+a_(s3) +a_(s4)) in which a_(s2) to a_(s4) are the cross-sectional areaof the second to fourth beads at the position examined. In general,A_(xn) =A_(on) -(a_(s1n) +. . . a_(sxn)), that is to say thecross-sectional area A_(xn) after bead x has been deposited at theposition n of the joint is the difference between A_(on) and the sum ofthe cross-section of all x beads at this position. The welding speedupon deposition of the following bead is a function of the residualcross-section which is to be filled with welding material. If thecross-section of a joint portion is less than a mean value, the weldingspeed in that joint portion should be greater than the welding portionswhich have wider cross-sections, and conversely. A uniform filling ofthe joint is obtained in this way. In practice, an exact determinationof the joint cross-section is not possible. In addition, the specifiedvalues for the cross-sectional area of the bead are not completelyreliable since the feed speed of the electrode is not constant. Asummation of these cross-sectional areas can lead to an erroraccumulation.

An edge offset generally occurs on butt-joint welding of large pipes orcylindrical containers. The cross-sections of the pipe or containerparts which are to be welded together always differ slightly from acircle shape and are elliptic or oval. When welding such workpiecestogether, it is not generally possible to bring the axis systems of theelliptic or oval cross-sections into coincidence with each other. Theresult of this is an edge offset in the joint, which changescontinuously along the whole joint. FIG. 2a shows, sightly exaggeratedin the axial direction, two cylindrical workpieces 12a, 12b with elipticcross-section in the butt-joint position. The edge offset along thesection I--I (FIG. 2b) of the two workpieces 12a, 12b is the opposite ofthat along the section II--II (FIG. 2c). As can be seen, the edge offsetvaries continuously around the periphery.

In most cases, only one root bead is applied in the joint base, fillingthe entire width of the joint. This is true in particular for V-typejoints, U-type joints and other similar joints. In the case of narrowsquare-butt joints, which are used in narrow-gap welding, thesquare-butt joint is provided on the root side (FIG. 3a) for examplewith a lip 13 delimiting a narrow gap 14. In another embodiment, thejoint is prepared as an open square-butt joint (FIG. 3b) with a backingstrip 15 being welded against the underside of the joint to serve as aweld support. In these joints, two base beads 16 and 17 are appliedalongside each other. These two base beads are welded at a predeterminedwelding speed, and a calculation of the welding speed on the basis ofthe calculated cross-sectional area in the joint portion is firststarted in conjunction with the deposition of the second bead, in whichrespect information for the deposition of the third bead is obtained.

it is advantageous to measure the contour of the joint using a sensorwhich, upon point contact with the joint contour, emits signalscorresponding to the coordinates of these points in the vertical andlateral directions of the joint. The sensor 18 shown slightlydiagrammatically in FIGS. 4 and 5 is provided with a feeler rod 19 witha ball-shaped tip 20. The feeler rod is fixed in a column 21 which isrotatable in a housing 22. The column is connected to a drive motor 23and can be rotated slightly more than 180°, as is shown by the brokenlines indicating the two end positions 24a, 24b of the rotationalmovement of rod 19. In another possible embodiment, the feeler rod ismuch longer and the rotational movement is limited to a smaller swingangle. A guide 25 with a rack 26 is secured to the housing 22, and agear wheel 28, driven by a motor 27, is in engagement with the rack 26.The guide 25 is displaceable in the vertical direction in a guide groove29 in a bracket 30, which supports the motor 27. The bracket isconnected securely to a welding burner 31 (indicated here onlydiagrammatically) which is provided with a feed mechanism (not shownhere) for a welding electrode 32, whose position has been indicated withbroken lines. The direction of welding is shown by an arrow 32a. Severalbeads 34 have already been deposited in the joint 33, and an additionalbead, which cannot be seen in FIG. 4, is being deposited using theelectrode 32.

During welding, the sensor scans the contour of the joint, that is tosay the sides 35a, 35b and the base 36 of the joint. For determining aspecific point, the sensor 18 is lowered until the tip 20 makes contactwith the base 36 of the joint, that is to say the topside of thedeposited beads 36 or the joint sides 35a, 35b. The height coordinate ofthe point is scanned by means of the rotational position of the motor 27which raises and lowers the feeler rod 19. The coordinate of the pointin the lateral direction of the joint is obtained from the rotationalposition 19 of the feeler rod.

A U-type joint 37 shown in perspective in FIG. 6 is partially filledwith a first bead 38. The deposition of a second bead 39 by means of anelectrode 40 is in progress. A number of points 41 on the base 42 and onthe sides 43a, 43b of the joint, whose positions are scanned by thesensor shown here by only its feeler rod 44, are marked by a +. Thesensor starts an oscillating movement at the base 42 of the joint at apoint 41a, is moved to the one joint side 43a and is moved upwards alongside 43a and past the joint edge 45a. At each point, the movement of thesensor as described above is repeated for determination of thecoordinates of the point. When the sensor has passed the joint edge 45a,the feeler rod upon its rotation in the lateral direction no longermakes contact with the workpiece, and no coordinate in the lateraldirection can be determined. In contrast, a height coordinate is scannedfor a point 41y on the topside 46a. As soon as this information isavailable, the sensor returns to a starting position 41b at the base 42of the joint. From there, the same measurement procedure is repeated onthe joint base 42 and the other joint side 43b (not shown here)including a point 41z on the topside 46b, after which the sensor isreturned to a new starting position 41c. During the measurement, thesensor has been moved along the joint at a specific and, whereappropriate, variable welding speed, so that the scanned points do notlie in one plane transverse to the longitudinal direction of the joint.Between the points 41a and 41c there extends a joint portion F₁ withinwhich the sensor effected the oscillating movement described above.

For a determination of the cross-section of the joint to be assatisfactory as possible, the coordinates of at least one point on eachjoint edge are required. A scanning of the exact position of the jointedge by means of the sensor is difficult to carry out. It isconsiderably simpler to determine this point by means of calculating aline 47 through two points 41₁, 41₂ set by their coordinates in thevicinity of the joint edge 45a. The point of intersection between thisline 47 and the plane which is represented by the topside 46a of thejoint is a point 48 on the joint edge 45a. The calculation of thecoordinates of this point is simple to carry out as the points 41₁ and41₂ and the associated joint edge 45a must lie in one plane. A point 48bis obtained on the other joint edge 45b in the same way.

The measured points include only the vertical and lateral coordinates.The scanned points can therefore be placed in a pane defined by thecoordinate axes and become, in this plane, the corner points of apolygon 49 (FIG. 6a). FIG. 6a is thus a section through al the points 41in the joint portion, in which respect the points have been projectedonto the coordinate plane. The deviation of the polygon from thegeometric shape of the joint, here the U-type joint, is generally quitesmall. By choosing a sufficiently large number of measurement points,the polygon 49 represents a mean value of the cross-sectional area ofthe joint for the whole of the joint portion scanned, which mean valueis satisfactory for determining the welding parameters.

When the sensor has effected its oscillating movement transverse to thejoint, the next oscillating movement is advantageously started within ajoint portion F₂ from the finishing position 41c of the sensor. It isalso possible for there to be pauses between the oscillating movementsof the sensor, for example when scanning those joints which have onlysmall variations in the joint cross-section between joint portions.

In joints with a simple geometric contour with planar joint sides, forexample a V-type joint (FIG. 7a), only the scanning of a small number ofpoints on the contour of the joint is required, since the deviations ofthe joint from the ideal shape generally relate only to the width of thejoint and an edge offset.

The workpieces 50a, 50b are to a slight extent mutually offset in thevertical direction. The joint surfaces 51a, 51b are planar, and theircontour can be determined simply by means of two points per joint side.Before welding is started, the sensor is swept over the joint in orderto determine a starting position 52, approximately above the middle ofthe joint. From this starting position the sensor begins all theoscillating movements in conjunction with the joint scanning. It shouldbe noted in this respect that the starting position is moved along thejoint at the welding speed.

The sensor is moved from the starting position first to the one topside53a and then to the other topside 53b, and the coordinates of the points54y, 54z on the top-sides are determined. The sensor is thereafter movedto the one joint side 51b, and a point 54b is scanned near the jointedge 55b, after which the sensor is moved to the root of the unfilledjoint. Because of the ball-shaped tip of the sensor, it is only possibleto obtain a measurement value of a point 54r in the vicinity of the rootand the narrow gap 55 is not scanned at all. Therefore, when calculatingthe cross-sectional area of the joint, it is expedient to make anaddition to the calculated area. The addition should correspond to theapproximate value of the area which the sensor cannot scan. Thecoordinates of the remaining points can be determined with greataccuracy, since it is possible to take account of the shape of the tipin the determination of the position of each of the remaining points.The sensor is then moved from the root upwards along the other jointside 51a, where a point 54a is measured, from there the sensor returnsto its starting position 52 which, as mentioned above, has meanwhilebeen moved along the joint a certain distance depending on the weldingspeed.

The points 54m, 54n on the two joint edges are determined by calculatingas described in conjunction with FIG. 6. The points 54m, 54n are,respectively, the points of intersection between the lines defined bythe points (54a, 54r); (54b, 54r) and the plane defined by the topside.

When the joint is filled with several beads (FIG. 7b), the joint contouris scanned in a similar manner as for the unfilled joint. The topside 57of the welding material is scanned at least by means of two points 58a,58b which indicate the position of the bead edge on the joint side.Since the topside 57 of the deposited welding material can be uneven, itmay be expedient to scan several points on this topside.

In FIG. 8, the enclosed area 59 of the joint 60 will generally representa polygon area P_(sn), where the first index refers to thecross-sectional area which is scanned in conjunction with the depositionof the s:th bead and n refers to the n:th joint portion, where thescanning was carried out. Thus, for example, P₁₃ refers to the meanvalue of the cross-section in the third joint portion, when the firstbead is deposited. Since the scanning of the joint takes place beforedeposition of the bead, P₁₃ also refers to a polygon area without anybead in the joint.

The first bead is deposited at a constant welding speed and at aconstant feed speed of the welding electrode. The cross-sectional areaof the first bead is therefore identical in size in all joint portionsand is here designated by a_(1n), in which the first index refers to thenumber of the bead and the second index to the number of the jointportion. Therefore, as regards the first bead, the following generallyapplies:

    a.sub.11 =a.sub.12 . . . =a.sub.1n

The corresponding cross-section residual areas for the determination ofthe welding parameter for the second bead are therefore:

    R.sub.21 =P.sub.11 -a.sub.11, R.sub.22 =P.sub.12 -a.sub.12. . . R.sub.2n =P.sub.1n 31 a.sub.1n

in the different joint portions 1, 2 . . . n, where P₁₁, P₁₂ . . .P_(1n) are measured polygon areas, a₁₁, a₁₂ . . . a_(1n) are thecross-sectional areas of joint portions 1-n of the first bead depositedwhich, in accordance with the above, is calculated from the feed speedof the electrode, the cross-section of the electrode, and the weldingspeed.

From these residual areas, R₂₁ -R_(2n) thus calculated, a mean residualarea value R_(2m) is formed, for which there is determined acorresponding welding parameter which controls the amount of thedeposited welding material per unit of length. Here, the welding speedis chosen as a variable welding parameter, while the feed speed of theelectrode is kept constant during the whole welding procedure. A weldingspeed V_(2m) corresponds to the mean value R_(2m). Upon deposition ofthe second bead, the welding speed V_(2n) in the respective jointportion n is calculated:

    V.sub.2n /V.sub.2m =R.sub.2m /R.sub.2n

On the basis of the different values of P_(sn), the welding speed isdifferent from one joint portion to the next. In FIG. 9 the weldingspeed is shown as a function of the joint portions. The mean value ofthe speed V_(sm) has been chosen with regard to the mean value R_(sm) ofthe residual areas. For welding technology reasons, the variations inthe welding speed should be kept within certain limits, which have beendesignated here by V_(max) and V_(min). The calculation is effected suchthat a mean value for the welding speed is chosen so that if possiblethe welding speeds for all joint portions, as calculated according tothe above formula, lie within the range defined by V_(max) and V_(min).However, as shown in FIG. 6 for example, the speed in a joint portionsometimes exceeds the maximum o falls below the minimum values for thespeed. The speed in joint portion 3 has a value which is greater thanV_(max). In such cases, a signal is triggered which, for example,informs the operator before the bead is deposited, that the weldingspeed at one or more joint portions will be too fast or too slow. Anumber of measures can be taken in order to rectify this problem. Forexample, one measure which can be taken is to limit the welding speed inthese joint portions to the permissible upper or lower limit value,since it can be expected that there will be a compensation upondeposition of the subsequent bead. However, large differences indicate aconsiderable error upon joint preparation which may not be correctablewith subsequent beads. In these cases, a correction is made by means ofa manual welding operation in the joint portion concerned, in whichrespect the automatic welding operation must be interrupted and startedup again after this joint correction.

On the basis of the speed calculated for these joint portions, thechange from one to the other joint portion should be effected in skips,as shown in FIG. 9. However, in practice, the speed is controlled insuch a way that there is a gradual, undisturbed transition from onespeed to the next, in which respect it is desired that the mean value ofthe speed in each joint portion should be equal to V_(sn). Thedifference between the calculated speeds of two adjoining joint portionsis generally small, and a transition between the speeds, adapted to thisdifference, is also selected with regard to the masses which must beaccelerated or decelerated.

it should be noted that the length of the joint portions is generallynot equal. Since the sensor is moved along the joint at a variablewelding speed, the distance along the joint, along which the sensoreffects one cycle of its oscillating movement, is also of unequallength.

In the case of weld joints in which the weld width increases from theroot to the topside, the number of beads per layer must be increased thecloser one comes to the topside. In the V-type joint (FIG. 10),deposited beads 61, 62 are shown in the first and second layers. At thethird layer the joint width is so great that two beads must be depositedin order to fill the whole layer.

The distance of the tip 63 of the electrode from one of the joint sideswill be a predetermined value S, when the bead 64 adjoining the jointside is deposited. If the distance is greater than the predeterminedvalue, the penetration of the bead into the base material is poor.

When the third bead 64 is deposited against the one joint side with theelectrode at a distance S from the joint side, the polygon area P_(3n)is measured simultaneously. This gives a value for a width b between thebead edges 65, 66 of the underlying bead 62. It has been found that onlyone bead per layer is required when k.b₁ <S, in which b₁ is theabove-mentioned joint width at the joint base in question, that is tosay the topside of the bead 62 before a new layer is deposited, and k isa factor between 0.5 and 1.0. Lower values for k are chosen in the caseof joints where the joint angle in the layer in question is small, forexample square-butt joints. In addition, the choice of the value of k isdetermined by one or more of the welding parameters, namely weldingvoltage, welding current, welding speed and electrode speed. The valueof k is determined by testing with smaller values for k giving greaterpenetration into the joint side, and vice versa.

Before the bead 64 is deposited, the points of the joint contour scannedby the sensor upon deposition of the bead 62 are taken as a basis forcalculating the polygon areas P₂₁ -P_(2n) and the corresponding residualareas R₃₁ -R_(3n) are calculated according to R_(3n) =P_(2n) -a_(2n), inwhich a_(2n) is the cross-section of the bead at joint portion n. Thepolygon areas P₂₁ -P_(2n) represent the area 67 framed by broken lines.

From the calculated residual areas for each joint portion, a mean valueR_(3m) is calculated, for which a mean speed V_(3m) is chosen. These twovalues will be valid for both beads 64, 68 in this layer. These meanvalues are therefore designated R_(pm) and V_(pm), in which the index pdesignates the number of the layer, here the third layer. Before thebead 64 is deposited, it is not possible to establish whether anadditional bead will be deposited in this layer. It is thereforeadvantageous for the calculation of the welding speed for all beads inthe same layer to start from a common mean value for the layer, namelyR_(pm) an V_(pm). The welding speed for the beads in the layer istherefore: ##EQU1## that is to say the welding speed in each jointportion is identical for both beads. The value of V_(pm) is chosen againwith regard to the spread of the different values V_(pn) in thedifferent joint portions, so that if possible no value of V_(pn) liesoutside the range defined by V_(max) and V_(min). Otherwise, a warningsignal is triggered.

In the case of joints with an edge offset, the above-mentionedcalculation leads to unfavorable results, and the calculation of thewelding speed must therefore be supplemented with a factor which takesaccount of the distribution of the welding material in the bead. Inorder to obtain a uniform distribution of the welding material in such ajoint (FIG. 11), for each joint portion a polygon area is calculated forthe left-hand and right-hand joint half. A center line 69, which dividesthe polygon area into two subpolygons, is drawn from the center point ofthe connection line between the joint edges to the joint center at theroot. The extent of this line is calculated with the aid of thecoordinates scanned by the sensor.

The subpolygon D_(2n1) and D_(2n2) where D_(2n1) +D_(2n2) =P_(2n),enclose the areas 70, 71 framed by the broken lines. The sub-polygonsare calculated when a new layer, here the third one, is to be deposited.The area of the subpolygons is reduced by an amount equal to half thecross-sectional area a_(2n) /2 of the last deposited second bead 74, sothat two partial residual areas are obtained: ##EQU2## The twosubpolygons form the basis for the calculation of the welding speed inthe joint portion n in the third layer of the joint, which comprises thetwo weld beads 72, 73.

The calculation of the welding speed for the two beads which aredeposited against the joint sides starts from the above-mentionedcalculation R_(pm) and a related welding speed V_(pm) for the two beadsin the layer. With regard to the edge offset which is expressed by thedisparity R_(pn1) =R_(pn2), the welding speeds for the two beads are nowcalculated in general by: ##EQU3## or according to FIG. 11: ##EQU4##

It should be noted that the first index after underlined designations Rand V refer to the number p of the layer, and after non-underlinedreferences to the number s of the bead.

The diagram of FIG. 12 shows an example of a relationship betweencalculated welding speeds for two beads in a layer at different jointportions F as well as the mean value V_(pm) of the welding speed and thepermitted limit values V_(max) and V_(min). The calculated weldingspeeds in each joint portion are shown on the one hand by full lines V₁for the one bead and by broken lines V₂ for the second bead. The beadwhich is deposited at a lower speed has a greater cross-section and istherefore applied against the joint side whose joint edge is situatedhigher. In joint portions 1 to 3, V₁ >V₂, and from joint portion 4onwards V₂ >V₁, which indicated that the edge offset from the jointportion 4 onwards is the opposite. It should be noted that the speedsshown here are calculated values. The transition between the calculatedspeeds of the joint portions is in practice effected continuously, andlikewise, the necessary change in speed is chosen with regard to themasses of the welding apparatus and/or workpieces which must beaccelerated or decelerated.

As a result of the above determination of the welding speed for the twobeads, the joint is filled uniformly despite the existing edge offset.

In a joint as shown in FIG. 13, one bead 74 in the first layer, one bead75 in the second layer, two beads 76, 77 in the third layer and twobeads 78, 79 in the fourth layer have been deposited. Two beads 80, 81have already been deposited in the fifth layer. The cross-sectional areaof the fifth layer is calculated as b₂.h, in which b is a mean value ofthe width of the joint at the level of the beads 80, 81 and h=(h₁ h₂)/2.The width of the topside of the layer formed by the beads 78, 79 hasbeen measured by the sensor. The incline of the joint side within thelayer which is to be deposited is also known. A mean value of the jointwidth in each joint portion can therefore be calculated. When the bead81 is deposited, the polygon area P_(8n), which is shown as enclosedarea 82, is scanned. The height h₁ of the bead 80 is determined with theaid of the coordinates which applied for the determination of thepolygon area P_(8n) and P_(7n). P_(7n) is the polygon area which wasscanned at the same time as the deposition of bead 80. The height h₁ isdetermined from these polygon areas at a certain distance from the jointside. The distance is advantageously equal to the distance S, which isthe stated distance of the tip of the electrode in the lateral directionfrom the joint side upon deposition of a bead adjoining the joint side.A height h₂ of the bead 82 deposited against the other joint side cannotbe determined in the same way, when only three beads are to be depositedin the layer. Determination of h₂ requires information on the polygonarea P_(9n), which is not available. It has been found that acalculation of the height h₂ according to the formula h₂ =h₁.a_(8n)/a_(7n) gives a satisfactory result for the calculation of the degree offilling. a_(7n) and a_(8n) are the known cross-sectional areas of thebeads 80 and 81 which have been deposited at a certain speed.

In FIG. 13 the ratios are such that the number of beads in the layer isthree. The number of beads in the layer (Z) is advantageously calculatedas follows:

    Z=2.b.sub.2 h/(a.sub.7n +a.sub.8n)

In FIG. 13 this value lies between 2.5 and 3.5. The value is rounded offin a known manner to 3. it may be advantageous to select the number ofbeads on the basis of a rounding-off calculation other than the normalone i.e., Z=H+d, in which H is the integer portion and d the decimalportion. It may be advantageous to choose (H+1) beads already whend>0.35 and not only when d>0.5.

The cross-sectional area of the third bead 83 indicated here in thelayer or the in-total ninth bead in the joint is a_(9n). Advantageouslya_(9n) =(a_(7n) +a_(8n))/2. The corresponding welding speed isproportional to the reciprocal value of a_(9n).

At the transition from one layer with three or more beads to a layerwith an additional bead, it is possible to determine the height h₂ ofthe bead deposited against the other joint side from the data on thecontour of the joint. This data includes values for the bead depositedagainst the other joint side which is obtained in conjunction with thedeposition of the third bead in the same layer. However, for practicalreasons, the same calculation method is used as in the deposition of thethird bead, that is to say the height h₂ is determined according to theformula given above.

In the case of a joint with an edge offset (FIG. 14) and several beadsper layer, the welding speed is determined for the two beads 84, 85adjoining the joint side in a new layer as a function of each subpolygonarea, which is derived from the polygon area which was calculated inconjunction with the deposition of the last bead 86 in the last layer.The polygon area is divided by the center line 87 into two halves whichin FIG. 14 have an area enclosed by a line 88, 89.

If the number of beads in the last layer is an odd number, in this casethree, each subpolygon area is reduced by an amount equal to half thecross-sectional area of the last-deposited bead 86, which in such a caseis always applied in the joint center, and the speed for the beads 84,85 is inversely proportional to these residual areas.

If the number of beads in the last layer is an even number, the polygonarea within which the main part of the last bead lies is reduced by thewhole of the cross-sectional area of this bead in order to obtain aresidual area, while the other subpolygon area is not reduced at all.

if the number of beads is even, the last bead lies to a very largeextent or completely within a single sub-polygon area. The residualareas corresponding to the welding speed of the two outermost beads inthe new layer are made up in one case of the whole subpolygon area andin another case by the subpolygon area which has been reduced by thecross-sectional area of the cross-section of the last bead fallingwithin the subpolygon.

The two possibilities for calculating the partial residua areas R_(pn1)and R_(pn2) for determination of the welding speed are thus as follows:

A) An odd number of beads has been deposited in the last layer ##EQU5##in which s is the number of the last bead and p is the number of the newlayer.

B) An even number of beads has been deposited in the last layer and thelast bead has, for example, been deposited within the outer subpolygonarea ##EQU6##

All these values of the areas according to A) and B) are present beforethe deposition of the first bead in the new layer. Before the depositionof the first bead in the new layer, a mean value R_(pm) of all theresidual areas R_(pn) of the joint portions is calculated, and a certainwelding speed is related to R_(pm), in which respect account is taken ofthe range within which the welding speed of all joint portions betweenV_(max) and V_(min) is to be situated.

The welding speeds for the two outermost beads in the new layer arethen: ##EQU7##

The cross-sectional areas corresponding to V_(pn1) and V_(pn2) are a₁and a₂.

For the beads which are to be deposited between the outer beads, thecross-sectional areas are calculated by linear interpolation, andcorresponding welding speeds are inversely proportional to thesecross-sectional areas.

When the welding of a layer has been finished, a check is made toascertain whether the next layer is to be a top layer which finishes thewelding operation. The mean value R_(pm) of the residual areas R_(pn) ofthe joint portions, which is shown by the enclosed area 90 in FIG. 15,is calculated, after which a quotient is calculated from this mean valueR_(pm) and the mean value of the cross-sectional areas of thelast-deposited intermediate layer in all joint portions. Such across-sectional area is shown by the crossed area 91 in FIG. 15. Whenthis quotient is less than 0.7, the next layer is the top layer. Sincethe top layer will also cover the joint edges, the number of beads ispreferably increased by one compared to the underlying intermediatelayer. Upon deposition of the two outer beads 92, 93, the electrode tip94 is held at a distance S₁ in the lateral direction from the jointsurface 95 or its imagined extension above the topside, which distanceis less than the above-mentioned distance S, that is to say S₁ <S (FIG.10). The distance S depends on the joint shape and is determined bytesting.

All the above-mentioned calculations are carried out in a microprocessor96 (FIG. 16) which constitutes part of the welding equipment. The sensor96 connected securely to a welding burner 97 emits signals correspondingto the scanned point coordinates. The microprocessor 96 receives thesignals, and on the basis of the information received, calculates,according to a program, the values for the welding speed in each jointportion, the number of beads per layer, etc. The results are convertedto signals which are transmitted to the supply unit 99 of the weldingburner and to the welding burner 97 which is provided with a feedmechanism (not shown here) for the welding electrode 100. Moreover, theposition of the sensor and of the welding burner in relation to thejoint is checked continuously, for example, for determining the positionof the joint portions as the scanning of the coordinates for calculationof the polygon areas progresses.

According to the above, the sensor carries out a comprehensivemeasurement program for determining the contour of the joint in eachjoint portion. These measurement values are also used for guiding thewelding burner along the joint.

In summary, one feature of the invention resides in a method forautomatic multi-run welding of a joint 33; 37 formed by two jointsurfaces, in which method the contour of the joint is scanned by asensor 18; 44 which emits signals corresponding to the contour of thejoint, which signals, after evaluation, control the deposition of theweld beads by mean of a continuously fed electrode 32; 40 which ismovable in at least three directions, and which is directed towards awelding point in the joint by an arc weld head 31 and is movedrelatively along the joint, characterized in that the sensor isoscillated in front of the weld head transverse to the joint atdifferent portions F₁, F₂ of the joint and is made to measurecoordinates in two directions, preferably in the vertical direction andlateral direction of the joint, of points 41 on the contour of the jointin question, which points essentially define the cross-section of thejoint, in that the area of the polygon defined by the coordinates ofthese points measured during one oscillating movement is calculated, andwelding parameters, which will control the amount of welding materialper unit of length in a bead to be deposited in the joint, aredetermined for the joint portions as a function of the correspondingpolygon area.

Another feature of the invention resides broadly in a method which ischaracterized in that the sensor is made to measure a coordinate in thevertical direction of a respective point 41y; 41z on each topside 46a;46b of the joint, and a line 47 is calculated between two measurementpoints 41₁, 41₂ on each joint side 43a, in which respect the point ofintersection of the line with the pane defined by the topside of thejoint is a point 48a; 48b of the joint edge 45a; 45b of thecorresponding joint side or a point of the polygon.

Yet another feature of the invention resides broadly in a method whichis characterized in that the sensor is oscillated during on-goingdeposition of a weld bead, in which respect at least the first bead inthe joint is deposited with a certain amount of welding material perunit of length, which amount is preferably identical for each jointportion.

A further feature of the invention resides broadly in a method which ischaracterized in that the welding parameters for each joint portion area function of the residual area calculated for the joint portion, thisresidual area being the difference between the calculated polygon areaand the corresponding cross-sectional area of the bead, whose depositionis in progress.

A yet further feature of the invention resides broadly in a method whichis characterized in that only one, and the same welding parameter isdetermined for each joint portion as a function of the polygon area, inwhich respect the welding parameter is either the welding speed or thefeed speed of the electrode.

Yet another further feature of the invention resides broadly in a methodwhich is characterized in that the welding parameter is the weldingspeed.

An additional feature of the invention resides broadly in a method whichis characterized in that a speed, corresponding to the mean value of thepolygon areas of the joint portions, for deposition of a certain amountof welding material per unit of length is determined, and in that thewelding speed for the different joint portions is calculated as afunction of the ratio between the polygon areas of the joint portionsand the mean value of the polygon area.

A yet additional feature of the invention resides broadly in a methodwhich is characterized in that a warning signal is triggered when thewelding speed for any joint portion has a value lying outside apredetermined value range comprising a maximum and minimum value.

A further additional feature of the invention resides broadly in amethod which is characterized in that the welding speed is a function ofthe residual area calculated for the joint portion and a function of thewelding speeds which have been calculated for the two adjoining jointportions.

A yet further additional feature of the invention resides broadly in amethod which is characterized in that a second weld bead 68 is depositedin the joint alongside the first bead 64 in order to form anintermediate layer, when the mean value of the values corresponding tothe width of the joint in the various joint portions at the level of thesaid intermediate layer is greater than a predetermined value.

Another further additional feature of the invention resides broadly in amethod which is characterized in that the value corresponding to thewidth of the joint is equal to k.b₁, in which k is a factor between 0.5and 1.0 and b₁ is the joint width at the bottom of the joint inquestion, and in that the predetermined value is a specific distance inthe lateral direction of the joint between the electrode tip 63 and thejoint surface.

A yet another additional feature of the invention resides broadly in amethod which is characterized in that the polygon defined by thecoordinates of the measurement points is divided by a center line 69through the joint into a first and a second subpolygon 70, 71 comprisingthe measurement points on each respective joint side and joint edge, andin that the welding parameters for the weld bead to be deposited againstthe respective joint side are determined for the joint portions as afunction of the corresponding subpolygon area and of the cross-sectionalarea of the last-deposited bead 74 in the underlying layer.

Another yet further feature of the invention resides broadly in a methodwhich is characterized in that at least three beads are deposited in anintermediate layer, when the means of a value determined for each jointportion of the cross-sectional area of the intermediate layer is greaterthan a predetermined value, in that the number of beads in theintermediate layer is a function of the mean value, and in that thecross-sectional area of the third bead and where appropriate furtherbead in this layer is a function of the cross-sectional area of thefirst two beads 80, 81 in this layer which are deposited against thejoint sides.

A still further feature of the invention resides broadly in a methodwhich is characterized in that the determined value of thecross-sectional area of the intermediate layer in each joint portion iscalculated as a function of the width b₂ of the intermediate layer andthe mean value of a measured height h₁ of the bead 80 deposited first inthis layer and against the one joint side at a specific distance S fromthe joint side, and of a calculated height h₂ of the bead 81 depositedimmediately thereafter against the other joint side, in which respect h₂=(h₁.a₂)/a₁, in which a₁ and a₂ are the corresponding cross-sectionalareas of the two deposited beads.

Still another further feature of the invention resides broadly in amethod in which the cross-sectional area of the intermediate layer isb₂.h, in which respect b₂ is the width of the said intermediate layerand h=(h₁ h₂)/2, and in that the number of beads per layer Z iscalculated as follows:

    Z=2.b.sub.2 h/(a.sub.1 +a.sub.2)

in which respect Z is rounded off to the nearest whole number.

Another still further additional feature of the invention residesbroadly in a method which is characterized in that the polygon definedby the coordinates of the measurement points is divided by a center line86 through the joint into a first and second subpolygon 87, 88comprising the measurement points of each respective joint side andjoint edge, and in that the welding speed for the weld bead 83, 84 to bedeposited against the one joint side or the other is determined for eachjoint portion as a function of the corresponding subpolygon area 87, 88and of the cross-sectional area of the last-deposited bead 85 in theunderlying layer, in which respect the cross-sectional areas of thefurther beads in the same intermediate layer are obtained byinterpolation with regard to the cross-sectional areas of the two beadsdeposited against the joint sides, and the corresponding welding speedsare inversely proportional to the cross-sectional areas.

Yet another still further additional feature of the invention residesbroadly in a method which is characterized in that, upon deposition oftwo or more beads per layer, before deposition of the first bead in anew layer a mean value R_(pm) of the residual areas R_(pn) of the jointportions is calculated and a specific welding speed V_(pm), whichcorresponds to the cross-sectional area a_(pm) of th welding material,is related to the residual area R_(pm), and the welding speed V_(pn)which corresponds to a cross-sectional area a_(pn1) for the bead againstthe one joint side and V_(pn) which corresponds to a cross-sectionalarea a_(pn2) for the bead against the other joint side, which weldingspeeds are determined as functions of the corresponding residual areaswhich are a function of the subpolygon areas and the cross-sectionalarea of the last-deposited bead in the underlying layer R_(pn1) orR_(pn2), respectively as follows: ##EQU8## in which respect thecross-sectional areas for the welding material for the intermediatebeads are obtained by interpolation, and the corresponding weldingspeeds are inversely proportional to these cross-sectional areas.

Still another yet further additional feature of the invention residesbroadly in a method which is characterized in that, after deposition ofan intermediate layer in the joint and before deposition of the nextlayer, a quotient is calculated from the mean value of the residualareas of the joint portions of the remaining joint cross-section 89 andthe mean value of the cross-sectional areas 90 of the last-depositedintermediate layer in all joint portions, and in that top beads for atop layer are deposited in the joint on this intermediate layer, whenthe quotient is less than a predetermined value, preferably less than0.7, in which respect the number of beads in the top layer is preferablyincreased by one compared to the number in the last depositedintermediate layer.

Art hereby incorporated as reference includes U.S. Pat. Nos. 4,302,655to Edling; 4,394,559 to Nomura et al.; 4,477,713 to Cook et al.; and4,491,718 also to Cook et al.

All, or substantially all, of the components and methods of the variousembodiments may be used with at least one embodiment or all of theembodiments, if any, described herein.

All of the patents, patent applications and publications recited herein,if any, are hereby incorporated by reference as if set forth in theirentirety herein.

The details in the patents, patent applications and publications may beconsidered to be incorporable, at applicants' option, into the claimsduring prosecution as further limitations in the claims to patentablydistinguish any amended claims from any applied prior art.

The invention as described hereinabove in the context of the preferredembodiments is not to be taken as limited to all of the provided derailsthereof, since modifications and variations thereof may be made withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A method for automatic multi-run welding of ajoint formed between at least two adjacent pieces to be welded by a weldhead to form a weld, each of the at least two adjacent pieces comprisinga joint surface, each joint surface being disposed for being welded toat least one adjacent joint surface, said method comprising the stepsof:scanning each of the adjacent joint surfaces of the joint with sensormeans, said scanning comprising scanning the joint in a plurality ofscans of said sensor means along the joint, said scanning for sensingeach said adjacent joint surface at a plurality of points on each saidadjacent joint surface during each scan of said plurality of scans, eachscan comprising a non-oscillating scan of each joint surface; generatingdata corresponding to coordinates of said plurality of points from eachscan; calculating with said data to obtain values indicative of at leasta part of a cross-section of at least a portion of the joint for eachscan of said sensor means along the joint; calculating at least a partof a cross-sectional area of said at least a part of a cross-section;adjusting at least one of:a speed of feed of a solid welding materialbeing fed into the weld, and a relative speed of movement between theweld head and the at least two adjacent pieces, by using said obtainedvalues indicative of said at least a part of a cross-section to controlthe amount of solid welding material deposited along said at least aportion of the joint; and depositing at least two beads of solid weldingmaterial along said at least a portion of the joint during at least tworuns of said weld head along the joint.
 2. The method for automaticmulti-fun welding of a joint according to claim 1, wherein:each of saidat least two adjacent pieces comprise a top surface substantiallytransverse to the joint surface; said sensor means is mounted in frontof the solid welding material for scanning the joint surfaces and thetop surfaces; and said sensor means comprises means for directlymechanically contacting the joint surfaces and the top surfaces beforeat least a portion of the joint is welded.
 3. The method for automaticmulti-run welding of a joint according to claim 2, furthercomprising:obtaining at least one coordinate of at least one point oneach said top surface, said at least one point on each said top surfacebeing in proximity of an intersection of each said top surface and thejoint surface; calculating a plane defined by the top surfaces by usingsaid at least one coordinate of said at least one point; calculating aline between at least two of said plurality of points on the jointsurface; and determining a point of intersection of said line with saidplane of the top surfaces, said point of intersection defining an edgepoint of an edge of the joint at the intersection of the top surface andthe joint surface.
 4. The method for automatic multi-run welding of ajoint according to claim 3, wherein said depositing at least two beadscomprises:depositing at least a first bead of solid welding materialalong said at least a portion of the joint, said at least a first beadof solid welding material comprising a fixed amount of solid weldingmaterial per unit length of the joint; said at least a portion of thejoint comprising a plurality of portions of the joint; continuouslyscanning the joint with said sensor means during said depositing of saidat least a first bead of solid welding material to directly measure aplurality of points in each of the plurality of portions of the joint;and depositing at least a second bead of solid welding material alongthe joint by adjusting said at least one of:said speed of feed, and saidrelative speed of movement, during said depositing of said at least asecond bead.
 5. The method for automatic multi-run welding of a jointaccording to claim 4, further including:calculating a cross-sectionalarea of the first bead of solid welding material; calculating across-sectional area for each portion of the plurality of portions ofthe joint; calculating a residual area for each portion of the pluralityof portions of the joint, said residual area being the differencebetween said calculated cross-sectional area of each portion of thejoint and said calculated cross-sectional area of the first bead ofsolid welding material deposited along the joint; calculating said speedof feed of a solid welding material being fed into the weld for eachportion of the joint as a function of said residual area; andcalculating said relative speed of movement between the weld head andthe two adjacent pieces for each portion of the joint as a function ofsaid residual area.
 6. The method for automatic multi-run welding of ajoint according to claim 5, further including:a) using only one of:saidspeed of feed of a solid welding material being fed into the weld, andsaid relative speed of movement between the weld head and the at leasttwo adjacent pieces, as a welding parameter to control the welding ineach the portion of the joint; and b) using the same said weldingparameter of step a) to control the welding in each portion of thejoint.
 7. The method for automatic multi-run welding of a jointaccording to claim 6, wherein said one welding parameter to control thewelding is said relative speed of movement between the weld head and theat east two adjacent pieces.
 8. The method for automatic multi-runwelding of a joint according to claim 7, further including:calculatingan average cross-sectional area for the joint from each saidcross-sectional area of each portion of the joint; calculating anaverage relative speed of movement between the weld head and the atleast two adjacent pieces for the joint, said average relative speedbeing a function of said average cross-sectional area; and calculating arelative speed of movement for each portion of the joint as a functionof the ratio between said cross-sectional area for the joint portion andsaid average cross-sectional area; and determining a range of speeds forsaid relative speed of movement between the weld head and the at leasttwo pieces, said range of speeds comprising a maximum speed above saidaverage relative speed of movement and a minimum speed below saidaverage relative speed of movement.
 9. The method for automaticmulti-run welding of a joint according to claim 8, further comprisingproducing a warning signal upon said relative speed of movement at leastone of:exceeding said maximum speed, and falling below said minimumspeed.
 10. The method for automatic multi-run welding of a jointaccording to claim 9, wherein said relative speed of movement for eachjoint portion is a function of said residual area calculated for thejoint portion and said relative speed of movement for each of apreceding joint portion and a following joint portion; anda transitionbetween a first relative speed of movement in a first joint portion anda second relative speed of movement in a second joint portion adjoiningthe first joint portion is effected gradually when said second relativespeed of movement is at least one of: greater than and less than saidfirst relative speed of movement.
 11. The method for automatic multi-runwelding of a joint according to claim 10, further comprising:determininga width of each portion of the joint at the base of the portion of thejoint; calculating a width value for each portion of the joint, saidwidth value being equal to k.b₁, in which k is a factor with apredetermined value between 0.5 and 1.0 and b₁ is the width of eachportion, and calculating an average width value of the joint from thewidth values of each of the joint portions;
 12. The method for automaticmulti-run welding of a joint according to claim 11, further includingdepositing additional beads of solid welding material along the joint toform at least one intermediate layer of beads of weld material, theadditional bead being deposited being:alongside a previous bead of solidwelding material when the average width of the joint is greater than apredetermined value, on top of a previous bead of solid welding materialwhen the average width of the joint is less than a predetermined value,and on top of a previous bead of solid welding material when the averagewidth of the joint is equal to a predetermined value.
 13. The method forautomatic multi-run welding of a joint according to claim 12, whereinsaid plurality of points for each portion of the joint define apolygon;said polygon being further subdivided into a first and a secondsubpolygon by a centerline through the joint; and each said subpolygoncomprising the measured points one each respective joint surface andjoint edge.
 14. The method for automatic multi-run welding of a jointaccording to claim 13, further including:calculating a cross-sectionalarea of each said subpolygon; calculating a cross-sectional area of alast-deposited bead of welding material; determining said weldingparameters for depositing a bead of solid welding material against ajoint surface of a subpolygon as a function of the subpolygon area andof the cross-sectional area of a last-deposited bead in an underlyinglayer.
 15. The method for automatic multi-run welding of a jointaccording to claim 14, further including:determining the width (b₂) ofsaid intermediate layer of beads of weld material; depositing a firstbead of weld material along one joint surface of the joint; determininga cross-sectional area (a₁) of the first deposited bead of weldmaterial; determining a height of the first deposited bead of weldmaterial in said intermediate layer for each portion of the joint;calculating a mean value (h₁) for said height of the first depositedbead of weld material; depositing a second bead of weld material along asecond joint surface of the joint; determining a cross-sectional area(a₂) of the second deposited bead of weld material; calculating a heightof said second deposited bead of weld material using the equation -h₂=(h₁.a₂)/2 calculating an average height value (h) for the first and thesecond deposited beads of weld material by using the equation -h=(h₁+h₂)/2; and calculating an average area value for the cross-sectionalarea of said intermediate layer as a function of the product of saidwidth of said intermediate layer and said average height value.
 16. Themethod for automatic multi-run welding of a joint according to claim 15,further including:depositing at least three beads of weld material insaid intermediate layer when said average area value is greater than apredetermined value; calculating a number of beads (Z) of weld materialto be deposited in said intermediate layer by using the equation-Z=2.b₂h/(a₁ +a₂) and rounding off the resultant value of Z to the nearestinteger value; determining a number of additional beads of weld materialto be deposited between the first and the second beads of weld materialdeposited along the joint surfaces; determining a cross-sectional areaneeded for each additional bead of weld material to be deposited betweenthe first and the second beads of weld material by interpolation withrespect to the cross-sectional areas a₁ and a₂ of the first and thesecond beads of weld material deposited along the joint surfaces, anddepositing the additional beads of weld material in said intermediatelayer between the first and the second beads of weld material at arelative speed of movement which is inversely proportional to thecross-sectional area of the additional beads of weld material.
 17. Themethod for automatic multi-run welding of a joint according to claim 16,further comprising, before the deposition of a layer:calculating aresidual area (R_(pn)) in each portion of the joint for each layer whenthe layer is to receive more than two beads of weld material;calculating an average residual area (R_(pm)) for each layer from eachof said calculated residual areas; calculating an average relative speedof movement (V_(pm)) as a function of said average residual area;calculating a residual area (R_(pn1) and R_(n2)) for each of said firstsubpolygon and said second subpolygon; and calculating the relativespeed of movement for the deposition of the first and second beads ofweld material by using the equations: ##EQU9##
 18. The method forautomatic multi-run welding of a joint according to claim 16, furthercomprising:calculating a quotient for each portion of the joint in alast-deposited intermediate layer from the average residual area of eachportion of the joint in the last-deposited intermediate layer and saidaverage area value of the cross-sectional area in each portion of thejoint in the last-deposited intermediate layer; and depositing a toplayer of beads of weld material in the joint on the last-depositedintermediate layer when said quotient is less than a predeterminedvalue, the top layer of beads of weld material containing one more beadof weld material than the last-deposited intermediate layer. 19.Apparatus for automatic multi-run welding of a joint formed between atleast two adjacent pieces to be welded by a weld head to form a weld,each of the at least two adjacent pieces comprising a joint surface,each joint surface being disposed for being welded to at least oneadjacent joint surface, said apparatus comprising:a welding housing; aweld head disposed on the welding housing, the weld head comprisingmeans for receiving a solid welding medium and means for feeding thesolid welding medium to the weld; a welding power supply for providingcurrent for the weld head; means for providing relative movement betweenthe weld head and the at least two adjacent pieces; sensor means forscanning at least a portion of the joint, said sensor means being fordirectly measuring a plurality of actual points on each said jointsurface to generate data corresponding to coordinates of said points;means for oscillating said sensor means transverse to a longitudinalaxis of the joint to scan each said joint surface during at least ahalf-oscillation of said sensor means within said joint; processingmeans for receiving said data corresponding to coordinates of saidpoints, for calculating the cross-sectional area of the joint from saiddata corresponding to coordinates of said points, for calculating atleast one of:a speed of feed of the solid welding medium into the weld,and a relative speed of movement between the weld head and the at leasttwo adjacent pieces, and for producing signals for control of thewelding; said apparatus further comprising at least one of: means forcontrolling the means for feeding the weld rod to control the amount ofsolid welding material being fed into the weld, and means forcontrolling the means for providing relative movement between the weldhead and the at least two pieces to control the amount of solid weldingmaterial being deposited along the joint; and control means forreceiving said signals for control of the welding, and for controllingat least one of: said means for controlling the means for feeding theweld rod to control the amount of solid welding material being fed intothe weld, and said means for controlling the means for providingrelative movement between the weld head and the at least two pieces tocontrol the amount of solid welding material being deposited along thejoint.
 20. The apparatus for automatic multi-run welding of a jointaccording to claim 19, wherein:said sensor means is mounted in front ofthe weld head for scanning at least a portion of the joint before thewelding of at least a portion of the joint; and said sensor meanscomprises means for directly mechanically contacting each said jointsurface during oscillation of said sensor means to measure saidplurality of points.